a) Field of the Invention
The present invention relates to a gradient generator that delivers compositional varied effluents. Gradient generators are widely used in liquid chromatography, ultracentrifugation, and gel electrophoresis. These are the three most basic methods of separation in biochemical research. More specifically, the present invention relates to an improved gradient generator based on Bock-Ling's disclosure published in 1954 (1).
b) Prior Art and Related Art
The most widely used gradient generator at present is Parr's mixing-chamber gradient generator disclosed in 1954 (2) also. The advantage of Parr's device is that it is simple in structure and can work in both fully filled or partially filled situations; i.e., its capacity is variable, although it is made of rigid material. However, Parr's device can only form simple gradients; the speed of the gradient that can form and deliver is relatively slow, and it also needs motor-driven stirring. Bock-Ling's device, however, delivers effluents whose composition can vary in any controlled and predictable manner. This kind gradient generator has never been widely employed up to now, because the capacity of any given Bock-Ling's device is predetermined, has no flexibility (because it can only start to work when all its vessels are fully filled, and it is made of rigid material), but, on the other hand, the requirements of routine experiments to the capacity of even a given gradient generator are varied from time to time. Moreover, Bock-Ling's device is relatively difficult to manufacture and relatively difficult to clean up after using. In 1977, Andersons (3) first embodied and improved the simplest embodiment of Bock-Ling's disclosure, made its capacity seem more or less adjustable by changing the slope of the baffle in the rectangular tank. This kind gradient generator has only one type and one size, as shown in some company catalogs (4) since the 1980s. Both Parr's and Bock-Ling's devices could hardly work well when the employed gradient-forming liquids have a big difference of density.
U.S. Pat. No. 3,398,689 to Allington disclosed a 2-pump gradient generating apparatus, but it can only form liner gradient. This kind apparatus has been developed into a microprocessor controlled form and is very costly, even though they still can only form simple gradients such as liner gradient, stepwise gradient, or segmented gradient, and cannot form any more complex patterns of composition. In 1976, Lorentz (5) disclosed a method to roughly convert a stepwise gradient into a liner gradient in situ in glass tubes. Ten years later, Coombs employed a microprocessor-controlled motor to do the same job, and obtained U.S. Pat. No. 4,753,892. No device is known, however, that can form gradients accurately when the needed volume is very small.